Automated institutional and industrial ware-washing machines are generally configured with one wash tank for maintaining a readily available supply of a cleaning solution for use in the machine. During normal usage, at least a portion of, or all of, the used cleaning solution is discarded in order to keep the cleaning solution as clean as possible. Fresh water or other clean recycled water can be added to the wash tank to maintain an appropriate liquid level, thereby diluting the concentration of detergent in the solution. To obtain a cleaning solution at the most efficient cleaning concentration, a measured amount of a concentrated aqueous detergent solution can be periodically added to the reservoir by an auxiliary detergent dispenser where it is mixed with the fresh or recycled rinse water to form a cleaning solution of the desired strength.
Automated institutional and industrial ware washing machines can add a rinse aid to the rinse water to promote sheeting and reduce water spotting on the washed ware using an auxiliary rinse aid dispenser.
Automated institutional and industrial fabric washing machines typically create a new cleaning solution for each cleaning cycle to which is added detergent, bleach, fabric softener and other additives. Accordingly, fabric washing additives are added to the wash water by auxiliary dispensers.
Wash chemical dispensers, used in processes as described above, typically have been designed for automatic or semi-automatic operation. The automated dispensers eliminates the need for constant operator attention to the cleanliness of the wash water and concentration of cleaner in the wash tank. Further, automated dispensers minimize operator error due to operator misjudgment in timing or in the amount of wash chemical to be added to the wash tank, and provides greater accuracy in maintaining the optimum concentration level of wash chemicals in the system.
A number of different techniques have been developed and used for converting a solid wash chemical into a concentrated wash chemical solution. The majority of such devices have been designed to convert solid detergent from its "powdered" form. See for example Daley et al, U.S. Pat. No. 3,595,438, issued July 27, 1971; Moffet et al, U.S. Pat No. 4,020,865, issued May 3, 1977; and Larson et al, U.S. Pat. No. 4,063,663, issued Dec. 20, 1977. For this reason wash chemical dispensers will be discussed with respect to the dispensing of detergents.
One detergent dispenser technique for converting powdered detergent, is the so-called "water-in-reservoir" type. In the water-in-reservoir dispenser, the powdered detergent is completely submerged in an aqueous solution. A stand-pipe, usually located near the center of the dispenser tank, maintains a constant water/solution level within the dispenser tank. As water is added to the dispenser tank, a concentrated, often saturated detergent solution or slurry is formed by the swirling action or agitation of the powdered detergent by the injected water. The added water also causes a portion of the solution or slurry in the reservoir to flow into the stand-pipe, which supplies the wash tank of the washing apparatus with the wash chemical. Such techniques are not practical for use with powdered detergents containing incompatible components (such as an active chlorine source in combination with a defoamer) as they tend to react upon contact when in solution. Further, there may be safety hazards involved with the use of such dispensers. Charging or recharging of such dispensers requires an operator to place detergent directly into standing water. Since the water-in-reservoir type of dispeners are typically mounted at about eye level or higher with respect to the operator, any splashing or splattering caused by adding the detergent directly into the concentrated solution poses the danger of spraying concentrated detergent solution onto the eyes, face and skin of the operator.
Another technique for converting a powdered detergent into a concentrated detergent solution, involves the technique of placing the powdered detergent over the convex side of a conical or hemispherical screen having a mesh size smaller than the powdered detergent particles supported thereby. The powdered detergent which directly overlies the support screen is dissolved as needed, by a fine mist or spray of water from a nozzle disposed below and on the concave side of the screen. The concentrated detergent solution formed by the action of the water falls by gravity into an underling reservoir, or is directed by a conduit to the wash tank of the washing apparatus. (See, for example, U.S. Pat. Nos. 3,595,438 issued to Daley et al; 4,020,865 issued to Moffat et al; and 4,063,663 issued to Larson et al.) This technique solves many of the problems associated with the water-in-reservoir type of dispenser as (i) the entire charge of powdered detergent is not wetted, and (ii) an operator loading detergent into the dispenser is not placing detergent directly into standing water and therefore is not subjected to possible boil-over or splattering of the detergent solution.
While the powdered detergent dispensers such as described by the Daley, Moffat and Larson patents have represented significant contributions to the art of detergent dispensing, the use of solid detergent in powdered form has a number of drawbacks in commercial applications. Due to increased sanitary standards and demands for shorter wash times, recently developed powdered detergents have relatively more complex detergent compositions that are more hazardous to the user, less stable and more difficult to dissolve in a satisfactorily uniform manner. Powdered detergents dissolve generally readily because of their high specific surface areas. However, when such powdered detergents include a mixture of a number of components having relatively different dissolving rates, such detergents are susceptible to differential solubility problems in automatic detergent dispensers, depending upon the rate of dispensing or the residence (dwell) time of contact between the detergent powder and the dissolving liquid. Those particles having a greater rate of solubility and/or a greater specific surface tend to dissolve first, whereas those having a lower solubility rate and/or a lower specific surface tend to dissolve last. Another problem associated with powdered detergents is the incompatibility and/or instability of particular detergent components required for good cleaning action, when these components are mixed and added to a powdered detergent composition.
Another problem inherent in powdered detergent is segregation of different sized particles during manufacturing, shipping and handling. Even when uniform distribution can be achieved during manufacture, subsequent shipping and handling may cause segregation, leading to non-uniformity in the composition of the detergent when it is withdrawn from the container. Another disadvantage of powdered detergents when handled in bulk form is that they are quite susceptible to spillage onto the floor, on the washing machine, etc. by the user.
Another form of solid detergent is the briquette form, comprising pre-shaped briquettes of solid detergent. Dispensing systems for dissolving detergent briquettes are known in the art. See, for example, U.S. Pat. Nos. 2,382,163, 2,382,164 and 2,382,165 all issued Aug. 14, 1945 to MacMahon, and U.S. Pat. No. 2,412,819, issued Dec. 17, 1946 to MacMahon. In the MacMahon systems, the detergent briquettes are dispensed from a modified water-in-reservoir dispenser wherein a number of the briquettes are held in a mesh basket forming a slot across the diameter of the reservoir. A stream of water directed against the lowermost briquette, in combination with the swirling action of water engaging the submerged portion of the lower-most briquette provides the dissolving action. The primary advantage of using detergent briquettes in such dispensers is that the user can visually determine when the detergent dispenser reservoir needs a replenishing charge of detergent. As with the water-in-reservoir type of dispenser, however, water is left standing in the reservoir, and a portion of the briquettes are submerged within that water. Accordingly, where there are incompatible components within the detergent briquettes, there can be undesirable interaction therebetween. Further, if the detergent contains a defoamer, that defoamer tends to float to the top of the reservoir during periods of inactivity, forming a slag at the water surface. For these and other reasons, the briquette detergent approach has not attained that degree of commercial success in the conventional institutional and industrial washing machine art, as has the powdered detergent dispensing approach.
Still another, more recent form, of solid detergent is the "cast" or block form, comprising detergent cast within a mold or container. Dispensing systems for dissolving these cast solids are known in the art. See, for example, U.S. Pat. No. 4,426,362 issued to Copeland et al and commonly owned copending U.S. Pat. applications Ser. Nos. 234,940 and 509,916. The cast detergent is dispensed from a dispenser wherein a solvent is sprayed onto the detergent block held within its container, impinging upon at least one exposed surface of the detergent to form a concentrated working solution. The concentrated working solution falls into a reservoir or is directed by a conduit to the wash tank of the washing apparatus. When the chemical compound within the container is completely utilized, the exhausted container can be removed and a fresh container can be placed in the dispenser.
Additional features have been sought by users of solid block dispensers including (i) an increase in the number of solid blocks of detergent capable of being held by the dispenser (i.e the ability to add additional blocks without having to wait until the present block is completely used), (ii) providing a relatively constant wash chemical dispensing rate, and (iii) reducing the unit cost of the wash chemical.
Accordingly, a need exists for a dispensing apparatus which can simply, safely, efficiently and inexpensively dispense a homogeneous, uniform, concentrated wash chemical solution from a solid block of wash chemical at relatively constant concentrations.